PAs3S3 cage as a new building block in copper halide coordination polymers

First examples of the coordination chemistry of the PAs(3)S(3) cage were obtained from solutions of PAs(3)S(3)·W(CO)(5) (1) in CH(2)Cl(2) or CH(2)Cl(2)/toluene and CuX (X = Cl, Br, I) in MeCN through interdiffusion techniques. Crystals of [Cu(PAs(3)S(3))(4)]X (2, X = Cl; 3, X = Br) and [(Cu(2)I)(PAs(3)S(3))(3)]I (4) were obtained and characterized by Raman spectroscopy (2) and single-crystal X-ray crystallography. The solid-state structures reveal an unexpected coordination versatility of the PAs(3)S(3) ligand: apical phosphorus and bridging sulfur atoms interact with copper, while As···X interactions determine the dimensionality of the frameworks. The structures of 2 and 3 contain tetrahedral [(PAs(3)S(3))(4)Cu](+) cations as secondary building units (SBUs), which are arranged by interactions with Cl(-) or Br(-) anions into two- and three-dimensional substructures. These interpenetrate into a (2D + 3D) polycatenane. Compound 4 is built up by a one-dimensional [(Cu(2)I)(PAs(3)S(3))(3)](n)(n+) ribbon with PAs(3)S(3) cages as P,S-linkers. The As atoms of the exo PAs(3)S(4) linkers interact with iodide counterions (3.35 < d(As-I) < 3.59 ?). The resulting two-dimensional layer is organized by weak As···I interactions (d(As-I = 3.87 ?) into a 3D network.     

Proton affinities of polybenzenoid aromatic hydrocarbons and those with five-membered rings

Proton affinities of PAHs including one five-membered ring are calculated by using the AM1 Hamiltonian for the determination of ΔH_f^o of the neutral and protonated molecules. The calculated PAs are compared to experimental PAs measured by chemical ionization mass spectrometry, using a new method based on competition between charge transfer and proton transfer occurring during the ionization process. A procedure is proposed to validate AM1-calculated PAs from experimental PAs after rescaling the calculated and measured PA values. The site of protonation is first determined on the criterion of the lowest loss of aromaticity, then on the criterion of the largest HOMO coefficient. For indene, the corrected result is compared to an ab initio calculation at the MP2/6-31G^*//HF/6-31G^* level and to a DFT calculation at the B3LYP/6-31G^* and the B3LYP/6-311 + G^** levels. Five new PAs are thus established and one published experimental PA is revised. © 1997 by John Wiley & Sons, Inc.     

Suppression of realgar cage degradation during complexation: formation of hybrid coordination polymers with As4S4, PAs3S3, and Cu(I) halide building blocks

Realgar, As(4)S(4), reacts with Cr(CO)(5)THF under cage degradation to give As(4)S(3)·Cr(CO)(5) (1). The reverse structural change is found if solutions of 1 in CH(2)Cl(2) react with equimolar amounts of PAs(3)S(3)·W(CO)(5) and CuX (X = Cl, Br, I) in CH(3)CN under biphasic diffusion conditions. The resulting coordination polymers 2-4 contain a reconstituted realgar molecule along with the PAs(3)S(3) cage. The crystal structures of (CuX)(As(4)S(4))(PAs(3)S(3)) (X = Cl: 2; Br: 3) are characterized by one-dimensional (1D) (CuX)(As(4)S(4)) strands, which are formed by alternating As(4)S(4) cages and CuX dumbbells. Terminal PAs(3)S(3) molecules are coordinated to copper by apical phosphorus and bridging realgar through sulfur. The As(3) triangles of the resulting (CuX)(As(4)S(4))(PAs(3)S(3)) strands interact with halides of neighbored strands to give a folded three-dimensional (3D) network. The structure of (CuI)(3)(As(4)S(4))(PAs(3)S(3)) (4) contains 1D (Cu(3)I(3))(n) strands as backbones, which are bridged by sulfur atoms of two η(1:2)-As(4)S(4) molecules while PAs(3)S(3) confines the resulting sheet. The As(3) triangles at the surface of the layers interact with iodide of the next layer to form a layered 3D network.     

Methyl and phenyl substitution effects on the proton affinities of hydrides of first and second row elements and substituent effects on the proton affinities of ring carbons in benzene: a DFT study

Theoretical calculations using B3LYP density functional theory (DFT) with the 6-311++G(d,p) basis set have been performed to determine proton affinities (PAs) of a series of H-X compounds and the corresponding methyl- (H(3)C-X) and phenyl- (Ph-X) substituted derivatives with a variety of proton acceptor atoms, such as C, O, N, F, Si, P, S, Cl, etc. Our results illustrate an interesting substituent effect on PAs. The PAs of ring carbon atoms for a series of monosubstituted benzene molecules (Y-C(6)H(5); Y = F, Cl, CH(3), OCH(3), NH(2), PH(2), OH, SH, SiH(3), CN, CF(3), and NO(2)) have also been estimated. Correlations between proton affinities of H-X, H(3)C-X, and Ph-X and substituent effects on the PAs of the ring carbon atoms for a series of monosubstituted benzene molecules have been studied. It has been observed that substituent effects on the PAs of the ring carbon atoms follow a good Hammett-type correlation.     

Exploring Oxidative NHC-Catalysis as Organocatalytic Polymerization Strategy towards Polyamide Oligomers

The polycondensation of diamines and dialdehydes promoted by an N-heterocyclic carbene (NHC) catalyst in the presence of a quinone oxidant and hexafluoro-2-propanol (HFIP) is herein presented for the synthesis of oligomeric polyamides (PAs), which are obtained with a number-average molecular weight (M_n) in the range of 1.7–3.6 kg mol⁻¹ as determined by NMR analysis. In particular, the utilization of furanic dialdehyde monomers (2,5-diformylfuran, DFF; 5,5’-[oxybis(methylene)]bis[2-furaldehyde], OBFA) to access known and previously unreported biobased PAs is illustrated. The synthesis of higher molecular weight PAs (poly(decamethylene terephthalamide, PA10T, M_n = 62.8 kg mol⁻¹; poly(decamethylene 2,5-furandicarboxylamide, PA10F, M_n = 6.5 kg mol⁻¹) by a two-step polycondensation approach is also described. The thermal properties (TGA and DSC analyses) of the synthesized PAs are reported.     

Survey of the proton affinities of adenine, cytosine, thymine and uracil dideoxyribonucleosides, deoxyribonucleosides and ribonucleosides

The kinetic method was applied to the determination of the proton affinities (PAs) of modified deoxy- and dideoxyribonucleosides. A correlation between the measured PAs and the replacement of one of the three hydroxyl groups of the ribose unit is presented. A PA scale was obtained which shows that the replacement of the primary or of one or both secondary hydroxyl groups of a ribonucleoside with a hydrogen atom induces the lowering or the enhancement of the nucleoside PA, respectively. The scale extends over a very narrow range of approximately 2 kcal mol(-1), thus demonstrating the sensitivity of the kinetic method in the evaluation of small differences in thermodynamic parameters.     

Minimum proton affinity for efficient ionization with atmospheric pressure desorption/ionization on silicon mass spectrometry

We performed a systematic study using a set of compounds with different proton affinities (PAs) on the ionization in atmospheric pressure desorption/ionization on silicon mass spectrometry (AP-DIOS-MS). The compounds studied included various aromatic molecules of different sizes. The PAs of these compounds were calculated using ab initio and hybrid density functional theory calculations at the B3LYP/6-31G(d) level of theory. We observed that only compounds with relatively high PAs above a threshold value of 920-950 kJ/mol were efficiently ionized as protonated molecules under AP-DIOS conditions and produced very clean mass spectra.     

Pushing Up the Size Limit of Boron-doped peri-Acenes: Modular Synthesis and Characterizations

Heteroatom-doped peri-acenes (PAs) have recently attracted considerable attention considering their fascinating physical properties and chemical stability. However, the precise sole addition of boron atoms along the zigzag edges of PAs remains challenging, primarily due to the limited synthetic approach. Herein, we present a novel one-pot modular synthetic strategy toward unprecedented boron-doped PAs (B-PAs), including B-[4,2]PA ( 1 a-2 ), B-[4,3]PA ( 1 b-2 ) and B-[7,2]PA ( 1 c-3 ) derivatives, through efficient intramolecular electrophilic borylation. Their chemical structures are unequivocally confirmed with a combination of mass spectrometry, NMR, and single-crystal X-ray diffraction analysis. Notably, 1 b-2 exhibits an almost planar geometry, whereas 1 a-2 displays a distinctive bowl-like distortion. Furthermore, the optoelectronic properties of this series of B-PAs are thoroughly investigated by UV/Vis absorption and fluorescence spectroscopy combined with DFT calculation. Compared with their parent all-carbon analogs, the obtained B-PAs exhibit high stability, wide energy gaps, and high photoluminescence quantum yields of up to 84 %. This study reveals the exceptional ability of boron doping to finely tune the physicochemical properties of PAs, showcasing their potential applications in optoelectronics.     

A rapid and highly specific method to evaluate the presence of pyrrolizidine alkaloids in Borago officinalis seed oil

Pyrrolizidine alkaloids (PAs) are complex molecules, present in plants as free bases and N‐oxides. They are known for their hepatotoxicity, and consequently there is a health risk associated with the use of medicinal herbs that contain PAs. Unfortunately, there is no international regulation of PAs in foods, unlike those for herbs and medicines: in particular, for herbal preparation or herbal extracts, the total PA content must not exceed 1 µg/kg or 1 µg/l, respectively. Borago officinalis seed oil is a source of γ‐linolenic acid, and its use is increased in both pharmaceutical and health food industries. Even if studies based on gas chromatography and TLC methods showed that PAs are not co‐extracted with oil, the development of a rapid and sensitive method able to evaluate the presence of PAs in commercially available products is surely of interest. The presence of PAs in a commercially available Borago officinalis seed oil was tested either in the oil sample diluted with tetrahydrofuran/methanol (MeOH)/H₂O (85/10/5 v:v:v) or after extraction with MeOH/H₂O (50/50 v:v) solution The samples were analysed by electrospray ionization in positive ion mode and in high mass resolution (60 000) conditions. In both cases to evaluate the effectiveness of the method, spiking experiments were performed adding known amount of two PA standards to the borage seed oil. A limit of detection in the order of 200 ppt was determined for these two compounds, strongly analogous to Borago officinalis seed oil PAs. Consequently, if present, PAs level in Borago officinalis seed oil must lower than 200 ppt. Copyright © 2013 John Wiley & Sons, Ltd.     

Peptide amphiphile nanofibers with conjugated polydiacetylene backbones in their core

The coupling of electronic and biological functionality through self-assembly is an interesting target in supramolecular chemistry. We report here on a set of diacetylene-derivatized peptide amphiphiles (PAs) that react to form conjugated polydiacetylene backbones following self-assembly into cylindrical nanofibers. The polymerization reaction yields highly conjugated backbones when the peptidic segment of the PAs has a linear, as opposed to a branched, architecture. Given the topotactic nature of the polymerization, these results suggest that a high degree of internal order exists in the supramolecular nanofibers formed by the linear PA. On the basis of microscopy, the formation of a polydiacetylene backbone to covalently connect the beta-sheets that help form the fibers does not disrupt the fiber shape. Interestingly, we observe the appearance of a polydiacetylene (PDA) circular dichroism band at 547 nm in linear PA nanofibers suggesting the conjugated backbone in the core of the nanostructures is twisted. We believe this CD signal is due to chiral induction by the beta-sheets, which are normally twisted in helical fashion. Heating and cooling shows simultaneous changes in beta-sheet and conjugated backbone structure, indicating they are both correlated. At the same time, poor polymerization in nanofibers formed by branched PAs indicates that less internal order exists in these nanostructures and, as expected, then a circular dichroism signal is not observed for the conjugated backbone. The general variety of materials investigated here has the obvious potential to couple electronic properties and in vitro bioactivity. Furthermore, the polymerization of monomers in peptide amphiphile assemblies by a rigid conjugated backbone also leads to mechanical robustness and insolubility, two properties that may be important for the patterning of these materials at the cellular scale.     

“一锅法”制备氨基碳纳米管功能化磁性纳米粒子及其在谷物和蔬菜中苯氧羧酸类除草剂测定中的应用北大核心CSCD

有效萃取是分析复杂样品中苯氧羧酸类除草剂(PAs)残留的关键步骤。为此,该文利用“一锅法”水热技术快速、简便地制备了氨基碳纳米管功能化磁性纳米粒子(NH-CNTs@M)并作为磁固相萃取(MSPE)的萃取介质,用于萃取谷物和蔬菜样品中痕量PAs。研究利用多种手段对NH-CNTs@M的形貌、尺寸、磁性性质等进行了表征,结果表明FeO的粒径、氨基化碳纳米管的直径以及NH-CNTs@M的磁饱和值分别为30 nm、40 nm和44.2 emu/g。详细考察了制备条件和萃取参数对NH-CNTs@M/MSPE萃取性能的影响,结果表明,NH-CNTs@M/MSPE可通过π-π、疏水和氢键作用有效富集目标化合物,最佳萃取条件如下:吸附剂用量为30 mg,解吸溶剂为含2.0%(v/v)甲酸的乙腈溶液,吸附时间和解吸时间分别为8.0 min和3.0 min,基底pH值为6.0,不调节基底的离子强度。将NH-CNTs@M/MSPE与高效液相色谱-二极管阵列检测技术(HPLC-DAD)联用,建立了谷物和蔬菜中PAs的灵敏检测方法。谷物和蔬菜基质中苯氧羧酸类除草剂的检出限(LOD,S/N=3)分别为0.32~1.6μg/kg和0.53~1.6μg/kg,定量限(LOQ,S/N=10)分别为0.94~4.8μg/kg和1.6~4.8μg/kg。在两种实际样品中不同浓度下的加标回收率分别为73.1%~112%和72.3%~113%。与现有方法相比,所建方法具有萃取速度快、灵敏度高和环境友好等特点。     

Molecular structure of helical supramolecular dendrimers

The molecular structure of helical supramolecular dendrimers generated from self-assembling dendrons and dendrimers and from self-organizable dendronized polymers was elucidated for the first time by the simulation of the X-ray diffraction patterns of their oriented fibers. These simulations were based on helical diffraction theory applied to simplified atomic helical models, followed by Cerius2 calculations based on their complete molecular helical structures. Hundreds of samples were screened until a library containing 14 supramolecular dendrimers and dendronized polymers provided a sufficient number of helical features in the X-ray diffraction pattern of their oriented fibers. This combination of techniques provided examples of single-9(2) and -11(3) helices, triple-6(1), -8(1), -9(1), and -12(1) helices, and an octa-32(1) helix that were assembled from crownlike dendrimers, hollow and nonhollow supramolecular crownlike dendrimers, hollow and nonhollow supramolecular disklike dendrimers, and hollow and nonhollow supramolecular and macromolecular helicene-like architectures. The method elaborated here for the determination of the molecular helix structure was transplanted from the field of structural biology and will be applicable to other classes of synthetic helical assemblies. The determination of the molecular structure of helical supramolecular assemblies is expected to provide an additional level of precision in the design of helical functional assemblies resembling those from biological systems.     

Highly twisted helical polyacetylene with morphology free from the bundle of fibrils synthesized in chiral nematic liquid crystal reaction field

We synthesized novel axially chiral binaphthyl derivatives with highly twisting powers by substituting phenylcyclohexyl (PCH) mesogenic moieties into 2,2' positions or 2,2',6,6' positions of binaphthyl rings. The di- and tetrasubstituted binaphthyl derivatives, abbreviated as D-1 and D-2, respectively, were adopted as chiral dopants to induce chiral nematic liquid crystals (N*-LCs) available for synthesis of helical polyacetylene. The helical twisting power (betaM) of D-2 was 449 microm(-1), which was ca. 2.6 times larger than that of D-1 (171 microm(-1)). We prepared two kinds of induced N*-LCs with 5 microm and 270 nm in helical pitch by adding the chiral dopants D-1 and D-2 into the host N-LCs, respectively. The helical polyacetylene synthesized in the N*-LC containing D-2 exhibited highly screwed fibrils, but not a bundle of fibrils. This result is in quite contrast to the usual fibril morphology, where the screwed fibrils are gathered to form the bundle of fibrils, as observed in the helical polyacetylene synthesized in the N*-LC containing a chiral dopant with moderate helical twisting power, such as D-1. It is of keen interest that the helical pitch (270 nm) of the N*-LC including D-2 is much smaller than the diameter (ca. 1 microm) of the bundle of fibrils, which should depress the formation of the bundle of fibrils. The morphology free from the bundle of fibrils might enable us to evaluate more precisely intrinsic electromagnetic properties of a single screwed fibril of helical polyacetylene.     

Chiral amplification in macromolecular helicity assisted by noncovalent interaction with achiral amines and memory of the helical chirality

Poly[(4-carboxyphenyl)acetylene] (poly-1) exhibits an intense induced circular dichroism (ICD) in the UV-visible region upon complexation with excess (R)-1-(1-naphthyl)ethylamine ((R)-2), owing to the formation of a predominantly single-handed helical conformation of the polymer backbone. In the presence of a small amount of (R)-2, poly-1 showed a very weak ICD due to the lack of a single-handed helical conformation. However, we have found that the co-addition of the excess bulky, achiral 1-naphthylmethylamine (5) with a small amount of (R)-2 caused a dramatic increase in the ICD magnitude, comparable to the full ICD induced by excess (R)-2. This indicates that an almost single-handed helix can be induced on poly-1 upon complexation with a small amount of (R)-2 assisted by achiral 5. Furthermore, the induced single-handed helical poly-1 could be successfully memorized by the replacement of (R)-2 and 5 with achiral 2-aminoethanol or n-butylamine.     

Preparation and characterization of novel thermostable polyamides bearing different photoactive pendent architectures with antibacterial properties

Three diamine monomers with different derivatives of imidazole heterocyclic ring, aryl ethers and electron withdrawing trifluoromethyl groups in the backbone were synthesized and used in polycodensation reaction with various aliphatic and aromatic dicarboxylic acids for preparation of a series of novel polyamides(PAs). The PAs were obtained in high yields and possessed inherent viscosities in the range of 0.26-0.75 d L/g. All of the polymers were amorphous in nature,showed outstanding solubility and could be easily dissolved in amide-type polar aprotic solvents. They showed good thermal stability with glass transition temperatures between 162-302 ℃. Thermogravimetric analysis showed that all polymers were stable, with 10% weight loss recorded above 421 ℃ in N_2 atmospheres. All the PAs presented fluorescence upon irradiation with ultraviolet light and thus showed promise for applications in electroluminescent devices. The monomers and PAs were also screened for antibacterial activity against Gram positive and Gram negative bacteria.     

Quantitative photometrische Bestimmung der Pyrrolizidinalkaloide in Symphity Radix

Zusammenfassung Eine bereits in der Literatur beschriebene Farbreaktion für 1,2-ungesättigte Pyrrolizidinalkaloide (PAs) wird zur Gehaltsbestimmung der toxischen PAs in Symphyti Radix herangezogen. Durch Veränderung einiger Versuchsparameter konnte die Erfassungsgrenze auf 1 Mikrogramm herabgesetzt und die Reproduzierbarkeit der Messung erheblich verbessert werden. Für die alkaloidreichen Beinwellwurzeln wurde eine einfache Extraktionsmethode validiert, die einen Nachweis von 10 ppm in einem Gramm getrockneter Droge gestattet (0,001%).

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Quantitative photometric determination of pyrrolizidine alkaloids in Symphyti Radix

Summary A colour reaction for unsaturated pyrrolizidine alkaloids (PAs), which has already been published, is used for spectrophotometric determination of the toxic PAs in Symphyti Radix (Symphytum officinale L., Boraginaceae). By changing several parameters it was possible to reduce the detection limit to 1 microgram and to improve significantly the reproducibility of the quantitative determination. For Symphyti Radix a simple extraction method allowing the detection of 10 ppm PAs in 1 gram dried drug (0.001%) was validaded.

     

Proton affinities of ketones, vicinal diketones and α-keto esters: a computational study

The proton affinities of seven different ketones, vicinal diketones, and α-keto esters (acetophenone, 2,2,2-trifluoroacetophenone, 2,3-butanedione, 1-phenyl-1,2-propanedione, methyl pyruvate, ethyl benzoylformate, and ketopantolactone) have been evaluated theoretically using the conventional ab initio HF and several post-HF methods (MP2, MP4, CCSD), density functional methods with the B3LYP hybrid functional, as well as some ab initio model chemistries [CBS-4M, G2(MP2), and G3(MP2)//B3LYP]. The chemical compounds studied are frequently used substrates in the asymmetric hydrogenation over chirally modified platinum catalysts where the protonation properties of the chiral modifier and the substrates are of great interest. In most cases, the proton affinities (PAs) evaluated with the CCSD/6-311+G(d,p)//B3LYP/TZVP and G2(MP2) methods are in good agreement with the existing experimental ones. However, the previously reported PA of 2,3-butanedione seems to be too high by 10-15 kJ mol⁻¹. The B3LYP/TZVP//B3LYP/TZVP and MP2/6-311+G(d,p)//B3LYP/TZVP model chemistries predict proton affinities that are systematically higher and lower than the experimental PAs, respectively. If proton affinities are evaluated as the average of the PAs calculated with these two theoretical methods a very good agreement with the experimental results is obtained. The mean absolute deviation (MAD) from experiment of this combination method for the PAs of 13 test molecules is 4.0 kJ mol⁻¹. For 9 molecules composed only of first-row atoms the MAD is 2.5 kJ mol⁻¹. The B3LYP/TZVP//B3LYP/TZVP and MP2/6-311+G(d,p)//B3LYP/TZVP methods provide significant savings in computational time and disk space compared to the CCSD/6-311+G(d,p)//B3LYP/TZVP and G2(MP2) models. Therefore, it is suggested that if no experimental or highly accurate theoretical data is available (due to computational cost), the proton affinities of similar compounds as investigated in this paper, can be evaluated with the combination method. For the studied molecules, this method gives the following PAs (in kJ mol⁻¹): 788 (2,3-butanedione, exptl 802); 798 (2,2,2-trifluoroacetophenone, exptl 799); 811 (ketopantolactone); 813 (methyl pyruvate); 825 (1-phenyl-1,2-propanedione); 862 (acetophenone, exptl 861); 865 (ethyl benzoylformate).     

Interplay between the diamine structure and absolute helicity in Ni-salen metallofoldamers

The nature of internal chiral diamines can greatly influence the ratio of helical diastereomers for Ni-salen based metallofoldamers. The diastereomer ratio is small for metallofoldamers derived from (1R, 2R)-cyclohexanediamine, (11R, 12R)-9,10-dihydro-9,10-ethanoanthracene-11,12-diamine, or (1R, 2R)-cyclopentanediamine. By contrast, the foldamer from (1S, 2S)-1,2-diphenylethylenediamine provides a relatively large bias (6 : 1) for the P-helical diastereomer as evidenced by NMR studies, chiroptical data, and X-ray studies. A model is proposed to explain the origin of the helical bias. These findings underscore the need to consider helical diastereomers in models for asymmetric induction in metal-salen catalyzed reactions.     

Trends in the monitoring of legacy and emerging organic pollutants in protected areas

Protected Areas (PAs) are locations for conservation, internationally recognized for their natural, ecological, and/or cultural values. Human presence in PAs is generally limited to minimal or banned exploitation of natural resources. However, different threats to PAs are evident as a result of short and long-range transport of organic pollutants of legacy and emerging concern. There has been a shift of interest in legacy pollutants such as persistent organic pollutants (POPs) to emerging compounds, resulting in a need for improved monitoring strategies in PAs. Here, we highlight the main advances in environmental analytical chemistry for legacy and emerging pollution monitoring in PAs. Trends in sampling, sample preparation and instrumental determination of multiclass organic pollutants in biotic and abiotic matrices are presented and discussed. Here, we considered the most relevant and recent literature regarding organic pollutants in PAs from terrestrial to aquatic landscapes collected within 2015 to the present time frame.